1. Field of the Invention
The present invention relates to a miniature diaphragm pump, and particularly to a miniature diaphragm pump with high pumping efficiency which is utilized for an instrument applying an air pressure, e.g., a sphygmomanometer, etc.
2. Description of the Prior Art
A miniature diaphragm pump is utilized for an instrument applying an air pressure such as a sphygmomanometer, etc. A miniature diaphragm pump of this type in the prior art is illustrated in FIG. 13, which is described in U.S. Pat. No. 4,801,249. Numeral 1E designates a miniature DC-motor, numeral 2E designates an output shaft of the DC-motor 1E, numeral 6E designates a first casing with a shape like a cup whose bottom surface is fixed to the motor 1E by screws, and numeral 30E designates a collar fixed to the output shaft 2E. Numeral 3E designates a drive shaft one end of which is fixed to the collar 30E in the state that the drive shaft 3E is inclined at a predetermined angle in respect to the axis of the output shaft 2E and the other end of which comes to a position on an extension line of the axis of the output shaft 2E. Numeral 31E designates a drive member having a disk-shaped portion 17E with three fitting holes 4E and a tubular supporting member 19E. The drive shaft 3E is slidably fitted to the tubular supporting member 19E of the drive member 31E. Numeral 7E designates a diaphragm body made of an elastic material such as soft rubber, etc. Numeral 32E designates three cup-type diaphragm portions each of which extends downwardly from the diaphragm body 7E and is formed to be integral with the diaphragm body 7E. Numeral 33E designates drive portions each of which is formed at a bottom of the respective diaphragm portion 32E. Numeral 34E designates a tubular valve body extending upwardly from the diaphragm body 7E, which is formed to be integral with the diaphragm body 7E. Each drive portion 33E is connected to the drive member 31E by pushing a head portion 39E thereof into the corresponding fitting hole 4E of the drive member 31E. Numeral 13E designates a second casing having three cylinder-like portions for fitting the diaphragm portions 32E thereto. The second casing 13E is fixed to the first casing 6E. Numeral 12E designates a cover member which is fixed to the second casing 13E through the diaphragm body 7E. Numeral 35E designates a valve casing which extends upwardly from the cover member 12E, and numeral 40E designates a common valve chamber which is formed in the valve casing 12E. Numeral 9E designates three pump chambers each of which is formed by a space surrounded with a bottom surface of the cover member 12E and the inner surface of the respective diaphragm portion 32E. Each of the pump chambers 9E is communicated with the common valve chamber 40E through the corresponding air passage groove 41E. The tubular valve body 34E is arranged in the vicinity of the air passage grooves 41E in the state that the valve body 34E is kept in close contact with the inner wall surface of the valve casing 35E to form a first check valve. Numeral 36E designates an air delivery port formed at the top of the valve casing 35E. Numeral 37E designates dish-type valve bodies made of the elastic material such as soft rubber or the like. Numeral 38E designates a plural number of air suction ports formed in the cover member 12E. The dish-type valve bodies 37E are attached to the cover member 12E in the vicinity of the air suction ports 38E in the state that each valve body 37E covers the air suction ports 38E to form a second check valve.
An operation of the miniature diaphragm pump of the prior art described above is explained below. When the motor 1E is energized and the output shaft 2E rotates, the collar 4E also rotates and the drive shaft 3E is thereby moved such that the upper end of the drive shaft BE functions as a pivot and the lower end of the drive shaft 3E performs a circular motion round the axis of the output shaft 2E. The disk-shaped portion 17E of the drive member 31E is moved upwardly and downwardly in connection with the circular motion of the drive shaft 3E, so that a cyclical volume change of each pump chamber 9E is caused by a reciprocating motion of the respective drive portion 33E in the axial direction of the motor 1E. That is, when one of the drive portions 33E is moved downwardly to increase the volume of the corresponding pump chamber 9E, an air pressure in the pump chamber 9E decreases, so that the tubular valve body 34E comes into contact with the inner wall surface of the valve casing 35E. At the same time, the corresponding dish-type valve body 37E is opened such that the air is supplied into the pump chamber 9E through the air suction ports 38E. On the other hand, when the drive portion 33E is moved upwardly to decrease the volume of the pump chamber 9E, the air pressure in the pump chamber 9E increases, so that the dish-type valve body 37E comes into contact with the cover member 12E to close the air suction ports 38E. At the same time, the tubular valve body 34E is spaced from the inner wall surface of the valve casing 35E by means of the air pressure to open the tubular valve body 34E, so that pressurized air in the pump chamber 9E is exhausted through the air passage grooves 41E to the delivery port 36E.
However, since the drive shaft 3E is connected to the collar 30E so as to incline in respect to the axis of the output shaft 2E, a considerable contact area for slidably connecting the drive shaft 3E to the tubular supporting member 19E of the drive member 31E is required for stably performing a pumping action of the miniature diaphragm pump. As a result, in this prior art, most of a space lied around the collar 30E between the disk-shaped portion 17E of the drive member 31E and the DC-motor 1E is not utilized for performing the pumping action. Therefore, it is desired to make the miniature diaphragm pump as a whole smaller by reducing the above useless space in the miniature diaphragm pump while keeping high pumping efficiency thereof.